GLASS AND GLAZING

The Romans used some glass windows, but glass really came into wide use with the stained windows in cathedrals of the Middle Ages and beyond. The following types of glass are common in buildings:

1. Float glass: the most common type of glass used in windows, not a safety glass, will break into large, dangerous pieces.
2. Heat strengthened (tempered) glass: a type of safety glass that breaks into many small pieces, can have imbedded wire also.
3. Laminated glass: a type of safety glass that breaks but stays together as a unit.

What are the Various Energy Saving Options for Glass?

The windows tend to lose lots of energy for most buildings. A typical building wall may have an R value of 20, while a window R value will be less than 1. So there have been many recent improvements in window technology for improved energy conservation:

1. Low e glass: low emissivity (low e) glass uses a thin coating on the inside of the window glass to increase R value by reducing radiant heat flow. These coatings are transparent to visible light and opaque to infrared light. On a typical double glazed insulated glass, the low e coating is on the inside faces of the glass.
2. Krypton gas fill: the air typically found in an insulated glass unit is replaced with Krypton gas, which is 12 times more dense than air and provides additional insulation value.
3. Tinted glass: since much of the energy use in commercial buildings is often for air conditioning, tinted glass reduces the ultraviolet and visible light that comes into the building interior, thus reducing the heat load.